Substantia nigra hyperechogenicity in healthy controls: a [¹⁸Fluoro] Dopa-PET follow-up study

In order to assess nigrostriatal function over time in healthy subjects with substantia nigra hyperechogenicity (SN+) believed to be at higher risk for Parkinson's disease (PD), ten healthy SN+ subjects underwent [(18)Fluoro] Dopa positron emission tomography (PET) twice-at baseline and after a mean of 7.3 years. Neurological examination took place at study inclusion followed by a structured telephone interview focusing on early Parkinsonian symptoms at the time point of second PET study and 3.5 years later. The [(18)Fluoro] Dopa uptake remained unchanged in eight of ten participants. In the other two subjects marked unilateral reduction of putaminal [(18)Fluoro] Dopa uptake ratios appeared over the time, followed by complaints of a clinically manifest PD in one. We suggest that the progressive pathological PET findings in 20 % and PD conversion in 10 % of our cohort may be in accordance with the presumed proportion of SN+ individuals eventually developing PD based on SN+ prevalence of 10 % within the healthy population, being ten times higher than PD prevalence in the age of over 60 years. Our findings hint towards a significance of SN+ indicating a high risk for PD in some extrapyramidally healthy SN+ individuals.